Scheduling method and apparatus for spatial reuse

ABSTRACT

A scheduling method of giving a chance for transmission to a plurality of terminals in the same time period, and a device therefor are provided. The scheduling method includes: transmitting first scheduling information to terminals in a network, the first scheduling information defining transmitting/receiving terminals and a transmission time period; receiving channel measurement information including inter-terminal interference information from the terminals in the network; and generating second scheduling information defining transmission time periods and a plurality of transmitting/receiving terminals that do not interfere with each other by using the channel measurement information.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and is a continuation of U.S. patentapplication Ser. No. 14/017,243 filed Sep. 3, 2013, which is acontinuation of U.S. patent application Ser. No. 12/814,392 filed Jun.11, 2010, which claims priority to and the benefit of Korean PatentApplication Nos. 10-2009-0051975, 10-2009-0079318, 10-2010-0011164,10-2010-0015960, and 10-2010-0055206, filed in the Korean IntellectualProperty Office on Jun. 11, 2009, Aug. 26, 2009, Feb. 5, 2010, Feb. 23,2010, and Jun. 11, 2010, respectively, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relate to a method and apparatus for schedulingdata transmission of terminals in WLAN and WPAN environments.

(b) Description of the Related Art

In a wireless communication system such as WLAN (wireless local areanetwork) or WPAN (wireless personal area network), a control stationsuch as an AP (access point) or a PNC (piconet cordinator) allocates achance for transmission to terminals according to a predetermined policyin a predetermined time period so as to enable the terminals to transmitdata without depending on a competitive way.

For example, an AP of WLAN classifies time periods into competitiveperiods and noncompetitive periods and gives an exclusive chance fortransmission to a specific terminal in a noncompetitive period by usinga polling method. That is, if the AP occupies a channel with the highestpriority for resource allocation and transmits a polling message toterminals, a terminal selected in advance starts to transmit dataimmediately upon receiving the polling message.

In such a general resource allocation method, during one chance fortransmission, one terminal is exclusively given a chance fortransmission. However, since a terminal having a highly-directionaltransmission capacity or reception capacity forms a narrow beam, evenwhen the terminal is transmitting or receiving data, other terminalsthat are not in the zone of the beam can perform datatransmission/reception without interfere with each other.

Nevertheless, since a wireless communication system according to therelated art gives a chance for transmission to only one terminal pair inthe same time period during resource allocation based on anoncompetitive method, it is not utilizing a merit of a terminal havinga highly-directional transmission/reception capacity as it should.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide a schedulingmethod and apparatus having advantages of giving a chance fortransmission to a plurality of terminals in the same time period.

An exemplary embodiment of the present invention provides a schedulingmethod of a control station including: transmitting first schedulinginformation to terminals in a network, the first scheduling informationdefining transmitting/receiving terminals and a transmission timeperiod; receiving channel measurement information includinginter-terminal interference information from the terminals in thenetwork; and generating second scheduling information definingtransmission time periods and a plurality of transmitting/receivingterminals that do not interfere with each other by using the channelmeasurement information.

Another exemplary embodiment of the present invention provides aterminal device including: a channel measuring unit configured tomeasure a transmission channel of a transmission terminal and areception terminal when the terminal device is not defined as thetransmission terminal or the reception terminal in schedulinginformation received from a control station; and an informationtransmitting unit configured to transmit channel measurement informationaccording to the measurement results to the control station, and toperform data transmission or ACK message transmission in a transmissiontime period defined in the scheduling information when the terminaldevice is defined as the transmission terminal or the reception terminalin the scheduling information.

According to the exemplary embodiments of the present invention, it ispossible to give a chance for transmission to a plurality of terminalpairs in the same time period in a noncompetitive transmission period,thereby improving the efficiency of data transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing illustrating an exemplary embodiment of atransmission-beam forming method to supplement or substitute foromni-directional transmission;

FIG. 2 and FIG. 3 are drawings illustrating other exemplary embodimentsof the transmission-beam forming method to supplement or substitute foromni-directional transmission;

FIG. 4 is a drawing illustrating a basic operaion of a scheduling methodaccording to an exemplary embodiment of the present invention;

FIG. 5 and FIG. 6 are drawings illustrating more specific examples of ascheduling operation of an AP and data transmission operations ofterminals in WLAN;

FIG. 7 is a flowchart illustrating sequential steps of a schedulingoperation of the control station;

FIG. 8 is a drawing illustrating a specific example of a procedure ofcollecting channel measurement information of a terminal;

FIG. 9 is a drawing illustrating an example of a result report message;

FIG. 10 is a drawing illustrating an example of scheduling information;

FIG. 11 is a drawing illustrating an operation when a scheduling methodaccording to an exemplary embodiment of the present invention is appliedto a PSMP operation of WLAN in more detail;

FIG. 12 is a drawing illustrating an example of a frame structure forresource allocation;

FIG. 13 to FIG. 16 are signal flow charts illustrating a stage ofcollecting channel measurement information and a stage of generatingscheduling information;

FIG. 17 is a drawing illustrating an example of a scheduling method forimproving the efficiency of spatial reuse;

FIG. 18 is a drawing illustrating the scheduling method of FIG. 17 inphases;

FIG. 19 is a drawing illustrating an example of a field structure ofscheduling information used in the scheduling method of FIG. 17 and FIG.18;

FIG. 20 is a drawing illustrating the structure of information used todetermine the characteristics of traffic for frame transmission;

FIG. 21 is a drawing illustrating a configuration of a control stationaccording to an exemplary embodiment of the present invention; and

FIG. 22 is a drawing illustrating a configuration of a terminalaccording to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In general, a communication system includes a transmitter and areceiver. The transmitter and the receiver are a transceiver thatsimultaneously perform a transmission function and a reception function,and are implemented in forms of user equipment and a control station ina mobile communication system. For ease of explanation, in the presentinvention, a terminal that transmits user data in a mobile communicationsystem is referred to as a transmission terminal, another terminal thatreceives user data from a transmission terminal is referred to as areception terminal, and an agent that controls data transmission of atransmission terminal and a reception terminal is referred to as acontrol station.

The control station can be called a base station (BS), an advanced basestation (ABS), an access point (AP), a piconet coordinator (PNC), etc.,and is a generic term for apparatuses taking a role of scheduling datatransmission times for terminals in a network. The terminal can becalled a mobile station (MS), an advanced mobile station (AMS), userequipment (UE), etc.

If a transmission beam zone of any one terminal pair of terminals havinghighly-directional transmitting/receiving capacities does not overlap atransmission beam zone of another terminal pair, even though the twoterminal pairs are close to each other, they can independently performdata transmission.

The present invention is based on this characteristic and proposes ascheduling method and device for giving a chance for transmission to aplurality of terminals in a noncompetitive transmission period. Since aplurality of terminals are given a chance for transmission in the sametransmission period, scheduling according to exemplary embodiments ofthe present invention is called scheduling for spatial reuse.

Hereinafter, for ease of explanation, a scheduling method and device ina WLAN environment will be frequently described. However, this is justone of various exemplary embodiment of the present invention. Thepresent invention is applicable to any kinds of wireless communicationsystems that support noncompetitive scheduling, for example, WPAN(wireless personal area network).

In the specification, the term ‘a terminal in a network’ means aterminal that is in a cell including a control station and issubstationally controlled by the control station, and a cell influencedby a control station is also referred to as a serving cell or effectivecell.

In the specification, the term ‘scheduling information’ is a genericterm for data including various kinds of information necessary forallowing data transmission of a specific terminal in a noncompetitivetransmission period, and may include a polling message of WLAN or ascheduling message of WPAN as specific examples.

Exemplary embodiments of the present invention will be described belowin detail with reference to accompanying drawings.

Transmission-Beam Forming Method of Control Station

In order to enable a control station in a wireless communication systemcapable of high-directional data transmission to effectively transmitscheduling information to terminals in a network, it is necessary tofind an additional transmission method to supplement an omni-directionaltransmission method.

For example, in a high frequency band such as a transmission band of 60GHz, since a distance by which data can be transmitted byomni-directional transmission is short, it is difficult to sufficientlytransmit scheduling information to all terminals in a network. For thisreason, it is necessary to use a basic omni-directional transmission andan additional transmission method to supplement the omni-directionaltransmission or to use a separate transmission method without using theomni-directional transmission.

FIG. 1 is a drawing illustrating an exemplary embodiment of atransmission-beam forming method to supplement or substitute foromni-directional transmission.

As seen from FIG. 1, a control station can omni-directionally transmitthe same scheduling information by using directional antennas having abeam width of 90 degrees. Terminals in a network can receive the samescheduling information form the control station through transmissionbeams formed as shown in FIG. 1 no matter which directions the terminalsare in.

FIG. 2 and FIG. 3 are drawings illustrating other exemplary embodimentsof the transmission-beam forming method to supplement or substitute foromni-directional transmission.

The control station may omni-directionally transmit data by using ahighly-directional antenna whose direction can be controlled.Alternatively, the control station may omni-directionally transmit databy using a plurality of independent highly-directional antennas. FIG. 2is a drawing illustrating an example of a transmission-beam formingmethod of sequentially transmitting scheduling information in alldirections with a plurality of directional antennas having a beam widthof 90°, and FIG. 3 is a drawing illustrating an example of atransmission-beam forming method of transmitting scheduling informationby using a multi-beam.

The examples of beam widths shown in FIG. 1, FIG. 2, and FIG. 3 areillustrative only. The direction of a beam width or the number of mainlobes of a multi-beam is not limited to the shown examples. Also, atransmission beam should not be formed in a two-dimensional plane asshown in FIGS. 1 to 3, but may be formed in three-dimensional space uponthe same principle.

Basic Operations of Control Station and Terminal

For understanding of the present invention, first, a schedulingoperation of the control station and data transmission operations ofterminals are schematically examined. FIG. 4 is a drawing illustrating abasic operaion of a scheduling method according to an exemplaryembodiment of the present invention.

If the control station omni-directionally transmits schedulinginformation by using the above-mentioned transmission-beam formingmethod, each of terminals analyzes the received scheduling informationto determine whether a service period for data transmission has beenallocated to the corresponding terminal.

FIG. 4 shows a specific example in which the same service period hasbeen allocated to two terminal pairs. In FIG. 4, on the basis of thescheduling information of the control station, a terminal pair composedof a first teminal and a second terminal and another terminal paircomposed of a third terminal and a fourth terminal can simultaneoulyperform data transmission in the same time period without interferingwith each other. The terminals may start data transmission immediatelyafter receiving the scheduling information, or may perform datatransmission in a specific time period defined in the schedulinginformation, or may perform data transmission in an arbitrary timesection of an allocated time period.

FIG. 5 and FIG. 6 are drawings illustrating more specific examples of ascheduling operation of an AP and data transmission operations ofterminals in WLAN.

As shown in FIG. 5, if the AP transmits a polling message to terminalsin the network, a chance for transmission is allocated to a firstterminal and a third terminal of the terminals receiving the pollingmessage, the first terminal and the third terminal being defined in thepolling message. The first terminal and the third terminal transmit datato the second terminal and the fourth terminal in a time periodallocated by the AP, respectively. If data reception is completed, thesecond terminal and the fourth terminal transmit messages (e.g., ACKmessages) to the first terminal and the third terminal to informcompletion of normal reception of data. The second terminal and thefourth terminal may transmit the ACK messages to the AP in addition tothe first terminal and the third terminal to inform completion of datatransmission. Alternatively, the ACK messages may be transmitted to theAP by the first terminal and the third terminal.

Also, as shown in FIG. 6, the AP may transmit a polling message todefine two transmission terminals and one reception terminal. In thiscase, if the AP transmits the polling message to the terminals in thenetwork, a chance for transmission is allocated to a first terminal anda second terminal of the terminals receiving the polling message, thefirst terminal and the second terminal being defined in the pollingmessage. The first terminal and the second terminal simultaneouslytransmit data to the third terminal in a time period allocated by theAP. Therefore, the data reception rate of the third terminal is twice ascompared to a reception terminal shown in FIG. 5. Although not shown, ifthe data reception is completed, the third terminal may transmit an ACKmessage to the first terminal and the second terminal to informcompletion of normal reception of the data. The third terminal maytransmit the ACK message to the AP in addition to the first terminal andthe second terminal. Alternatively, the ACK message may be transmittedto the AP by the first terminal and the second terminal.

A scheduling operation of the control station will be described below indetail. FIG. 7 is a flowchart illustrating sequential steps of ascheduling operation of the control station.

The control station transmits scheduling information to the terminals inthe network, the scheduling information defining one terminal to havetransmission authority in a specific time period control (S101). Thescheduling information includes information on the first terminal tohave transmission authority and the second terminal to receive data fromthe first terminal. As such terminal information, a terminalidentification means such as a MAC address or a FIN (flow identitynumber) may be used.

Each of the terminals analyzes the received scheduling information todetermine whether the corresponding terminal has data transmissionauthority or is a destination of data transmission (S102).

Since the scheduling information can be received and analyzed by notonly the terminals participating in the data transmission/reception butalso the other terminals, a terminal that requires participating in datatransmission/reception next time measures a channel in the specific timeperiod (S103), and informs the control station of a measured signallevel (or energy level) value and identification information on theterminal(s) having participated in the data reception in the specifictime period (S104).

The control station reflects the informed information when generatingnext scheduling information (S105). Specifically, when it is determinedfrom the received information (channel measurement information) that thesignal level value in the specific time period is enough low that datareception is possible and it is perceived that there is another terminalwho plans data transmission to the informant terminal, the controlstation generates the next scheduling information to allow a terminalpair of informant terminal and another terminal to perform datatransmission in a specific time period. Even though the signal levelvalue is equal to or greater than a reference value, if there is aterminal requiring data transmission, the control station may generatethe next scheduling information to allow the corresponding terminal toperform data transmission.

Since Steps S101 to S105 are repeatedly performed, it is possible tosimultaneously permit a plurality of terminal pairs a chance fortransmission in a specific time period.

The individual steps of FIG. 7 are generally classified into a stage forcollecting channel measurement information and a stage for generatingscheduling information, which will be described below in detail.

Stage for Collecting Channel Measurement Information (PreprocessingStage of Scheduling)

Before resources are allocated to the plurality o terminals, it shouldbe first checked whether interference will occur when terminals having achance for transmission transmit data. To this end, the control stationcollects predetermined channel measurement information from theterminals in the network and uses the collected channel measurementinformation to determine whether interference will occur.

In other words, if the terminals perform channel measurement in a timeperiod when data transmission is performed and transmit the channelmeasurement information to the control station, the control station usesthe received channel measurement information as basic data for the nextresource (time period) allocation. For example, in order to collect thechannel measurement information, the control station allocates a timeperiod for test message transmission to the second terminal whilerequesting the first terminal to perform channel measurement. The firstterminal performs channel measurement and transmits the channelmeasurement information to the control station while the second terminaltransmits the test message.

If it is assumed that the channel measurement information includesinformation on channel's energy level, the measured channel's energylevel that is equal to or lower than a predetermined threshold valuemeans that, even when the first terminal receives data from the thirdterminal while the second terminal transmits data, interference does notoccur.

However, requesting channel measurement does not necessarily need testmessage transmission. If a terminal to perform channel measurement canperceive data transmission of other terminals, channel measurement ispossible without using a separate test message. Also, the channelmeasurement of the terminal should not be necessarily performed by arequest of the control station but may be performed periodically or whena predetermined event occurs.

A procedure of collecting the channel measurement information will bedescribed below in detail by using a specific example.

All terminals in the network have the scheduling information (or channelallocation information) supplied form the control station. A terminalcan see which time periods the other terminals can transmit data insince the scheduling information includes not only information on achannel section allocated to the corresponding terminal but alsoinformation on channel sections allocated to the other terminals. Theterminals collect channel measurement information on the basis of thescheduling information.

FIG. 8 is a drawing illustrating a specific example of a procedure ofcollecting channel measurement information of a terminal.

In FIG. 8, a monitoring device ‘A’ and a monitoring device ‘B’ performchannel measurement in a time period when a source device transmits datato a destination device.

In the example of FIG. 8, the monitoring device ‘A’ cannot monitor dataframe transmission of the source device but the monitoring device ‘B’can monitor data frame transmission of the source device. In contrastwith this, the monitoring device ‘A’ and the monitoring device ‘B’ canmonitor ACK frame transmission of the destination device. An intervalbetween a period when the monitoring device ‘B’ monitors data frames anda period when the monitoring device ‘B’ monitors ACK frames is referredto as a shot interframe space (SIFS). Transmitting and monitoring of thedata frames and the ACK frames are performed during one channel timeallocation (CTA) period.

The monitoring device ‘A’ and the monitoring device ‘B’ transmitmonitored information to the control station. In the example of FIG. 8,the channel measurement information includes the monitored informationand may be included in a specific result report message and thentransmitted to the control station.

FIG. 9 is a drawing illustrating a PSMP-DLT measurement element as anexample of a result report message. The arrangement of individual fieldsconstituting the PSMP-DLT measurement element or the number of bitsallocated to each of the fields may be variously modified. An example ofchannel measurement information reported through the PSMP-DLTmeasurement element is shown in Table 1.

TABLE 1 Destination device(by Status index Source device(by source)destination) y1 Decode Decode y2 Decode Busy y3 Decode Idle y4 BusyDecode y5 Idle Decode y6 Idle Idle y7 unknown unknown

In Table 1, y1 to y7 are constant numbers that can be arbitrarilydefined, and any kinds of information, including the contents defined inTable 1, necessary for channel measurement result report may be definedas the contents of the status index. Further, in Table 1, the term ‘bysrc’ represents a channel status when the source device performs datatransmission and the term ‘by dest’ represents a channel status when thedestination device performs data transmission.

In Table 1, the status index represents a channel status as any one of‘Decode’, ‘Busy’, ‘Idle’, and ‘Unknown’ for source device anddestination device.

The term ‘Decode’ represents that a monitoring terminal can successivelyreceive frames transmitted by a transmission terminal with no errors.

The term ‘Idle’ represents that a monitored channel is idle in a channelmeasurement period.

The term ‘Busy’ represents that, assuming that a measurement period hadbeen allocated to only a terminal pair, while a monitoring terminal isbusy, decoding of frames has failed in the measurement period. In otherwords, the term ‘Busy’ represents that, while the monitored channel hasbeen busy, normal reception of frames has failed in the measurementperiod. The term ‘Busy’ may represent that an error has occurred duringframe reception or that the channel is busy regardless of whether anerror has occurred.

The term ‘Unknown’ represents that, while the monitored channel is busy,it cannot be seen whether the monitored channel is being used by thesource device or the destination device.

Table 1 shows an exemplary embodiment of the channel measurementinformation. Another exemplary embodiment of the channel measurementinformation may include a signal-to-noise ratio (SNR) or received signalstrength indication (RSI) instead of the above-mentioned channel status,or may further include at least one of the SNR and the RSI in additionto the above-mentioned channel status.

Stage of Generating Scheduling Information (Scheduling Stage)

The control station uses the channel measurement information collectedform the terminals to generate scheduling information for spatial reuse.

FIG. 10 is a drawing illustrating an example of scheduling information.Specifically, FIG. 10 shows an example of a polling message used in apower save multi-poll (PSMP) scheme of IEEE 802.11 WLAN. However, thisis just an example. The arrangement of individual fields constitutingthe scheduling information or the number of bits allocated to each ofthe fields may be variously modified.

PSMP-DLT (Power Save Multi-Poll Direct Link Transmission) Start Offsetfield indicates the start of the PSMP-DLT. The offset is specifiedrelative to the end of the PSMP frame. The first PSMP-DLT is scheduledto begin from the end of the last PSMP-DTT or PSMP-UTT described in thePSMP after a SIFS period ends.

The PSMP-DLT Duration field indicates the maximum length of a PSMP-DLTfor a terminal pair composed of a transmission terminal and a receptionterminal (or station pair). All transmissions by the transmissionterminal within the current PSMP sequence lie within the indicatedcontents in the PSMP-DLT.

The DLT_target_ID field contains the AID (Association ID) of thereception terminal to which the transmission terminal tries to sendframes when PSMP-DLT is used for individually addressed datatransmission. The DLT_target_ID field contains the unique ID assigned bythe control station when PSMP-DLT is used for group addressed datatransmission. In this case, the control station issues the unique IDrepresenting multicast/broadcast address when DLS Setup procedure isprocessed.

The 4-bit reason code field indicates what purpose this PSMP-DLT isallocated for. It is defined in Table 2.

TABLE 2 Reason code Meaning x0 frame transmission x1 measurement ofPilot frame transmission x2 reporting of channel status information x3Data transmission by spacial reuse x4-x15 Reserved

In Table 2, x0 to x15 are constant numbers that can be arbitrarilydefined, and any kinds of information, including the contents defined inTable 2, necessary for resource allocation may be defined as thecontents of the reason code.

In Table 2, the measurement of pilot frame transmission is used forother monitoring terminals to measure the channel status when thetransmission terminal transmits a pilot frame for measurement to thereception terminal.

When the reason code is set to x2, a terminal transmits channel statusreport information (or channel measurement information) withoutdepending on a PSMP operation.

PSMP-DLT Duration ID represents the time period composed of PSMP-DLTStart Offset and PSMP-DLT Duration. This value is used to indicatemeasured time period when a monitoring terminal reports the channelstatus information to the control station.

Next, a scheduling procedure of a PSMP operation of WLAN will bedescribed below briefly.

A PSMP-DLT is allocated for a terminal pair composed of two terminals,one of which is scheduled to transmit frames, and the other is scheduledto receive the frames. A transmission terminal may transmit frameswithin the PSMP-DLT without performing CCA (clear channel assessment)and regardless of NAV (network allocation vector) at the start of itsPSMP-DLT.

The terminal should complete data transmission within the allocatedPSMP-DLT, even if it has more data queued than can be transmitted duringits allocated PSMP-DLT.

A reception terminal receives frames during its scheduled PSMP-DLT,

and is not required to receive frames at other PSMP-DLTs while thereception terminal measures channel status information and reports themeasured statistics at other PSMP-DLTs in response to a request ofchannel status measurement.

FIG. 11 is a drawing illustrating an operation when a scheduling methodaccording to an exemplary embodiment of the present invention is appliedto a PSMP operation of WLAN in more detail.

In FIG. 11, resources that relate to a time period when downlinkcommunication is possible (downlink phase), a time period when uplinkcommunication is possible (uplink phase), and a time period when directcommunication is possible (directlink phase) are allocated to a firstterminal STA1. The resources allocated to the first terminal STA1 havethe same time periods as those allocated to a second terminal STA2.

Resource allocation for downlink communication is performed through aPSMP-DTT (PSMP-DTT1 and PSMP-DTT2 in FIG. 10), resource allocation foruplink communication is performed through a PSMP-UTT (PSMP-UTT1 andPSMP-UTT2 in FIG. 10) message, and resource allocation for directcommunication is performed through a PSMP-DLT (PSMP-DLT1 and PSMP-DLT2in FIG. 10) message.

The first terminal and the second terminal performs downlinktransmission of data, uplink transmission of data, and data transmissionthrough direct communication in the same time periods, respectively.

FIG. 12 is a drawing illustrating an example of a frame structure forresource allocation.

Specifically, FIG. 12 shows an example of a structure of a super framein a system in which resource allocation to channels is performed atsuper frame units.

As shown in FIG. 12, the time period of the super frame may be dividedinto a beacon transmission period, a contention area period (CAP), and achannel time allocation period (CTAP).

The super frame starts with beacon transmission and a beacon includesinformation on the structure of the super frame. The CAP is a periodwhen terminals transmit data in a competitive method based on CSMA/CA(carrier sense multiple access with collision avoidance). The CTAP is aperiod when terminals transmit data in time periods allocated by pollingor scheduling in a noncompetitive method. In order to preventneighboring super frames from overlapping, a guide time exists betweenthe super frames.

FIG. 12 shows just an example of a structure of a frame for allocatingresources to terminals. The scheduling method using spatial reuseaccording to the exemplary embodiment of the present invention can beapplied to any frame structures for scheduling transmission periods.

Specific Exemplary Embodiment of Scheduling Method

Hereinafter, the stage of collecting the channel measurementinformation, the stage of generating the scheduling information, and thedata transmission stage described above will be described by using adetailed example.

FIG. 13 to FIG. 16 are signal flow charts illustrating a stage ofcollecting channel measurement information and a stage of generatingscheduling information. In FIG. 13 to FIG. 16, CTA-S, CTA-D, CTA-R, andCTA-T indicate different terminals.

First, in FIG. 13, during first channel time allocation CTA₁, the CTA-Stransmits data frames to the CTA-D and the CTA-D transmits ACK frames tothe CTA-S in response thereto. Meanwhile, the CTA-R monitors the ACKframes and the CTA-T monitors the data frames, thereby collectingchannel measurement information. Here, it is assumed that the channelstatuses measured by the CTA-T and the CTA-R are ‘decode’ statuses.Accordingly, the CTA-T can receive the data frames with no errors whilethe CTA-S performs data transmission, and the CTA-D can receive the ACKframe with no errors while the CTA-D transmits the ACK frames.

The CTA-T and the CTA-R transmit channel measurement information, whichrepresents that the ‘by src’ and the ‘by dest’ are the ‘decode’ statusand the ‘decode’ status, to the control station. The control station maygenerate scheduling information for realizing spatial reuse shown inFIG. 15 with reference to the channel measurement information.

In the example of FIG. 14, the terminal pair composed of the CTA-S andthe CTA-D and the terminal pair composed of the CTA-R and the CTA-Thaving received the scheduling information of the control station startdata frame transmission during the first channel time allocation CTA₁.Specifically, the CTA-T receives a PLOP header or a MAC header includedin the scheduling information during a propagation period to confirmstart of data frame transmission of the CTA-S and to check the timeperiod that does not interrupt the data frame reception of the CTA-D.Therefore, in the example of FIG. 15, even if the CTA-T transmits thedata frames to the CTA-R when the CTA-S transmits the data frames to theCTA-D, interference therebetween does not occur.

Next, in FIG. 15, during the first channel time allocation CTA₁, theCTA-S transmits the data frames to the CTA-D and the CTA-D transmits theACK frames to the CTA-S in response thereto. Meanwhile, the CTA-Rmonitors the ACK frames and the CTA-T monitors the ACK frames and thedata frames together, thereby collecting the channel measurementinformation. Accordingly, both of the CTA-R and the CTA-T can receivethe ACK frames when the CTA-D transmits the ACK frames, which meansinterference may occur with respect to the ACK frames. The controlstation may generate scheduling information for realizing spatial reuseshown in FIG. 16 with reference to the channel measurement information.

In FIG. 16, the terminal pair composed of the CTA-S and the CTA-D andthe terminal pair composed of the CTA-R and the CTA-T having receivedthe scheduling information of the control station start data frametransmission during the first channel time allocation CTA₁.Specifically, the CTA-T receives a PLCP header or a MAC header includedin the scheduling information during a propagation period to confirmstart of data frame transmission of the CTA-S and to check the timeperiod that does not interrupt the data frame reception of the CTA-D.However, since interference may occur with respect to the ACK frames,the CTA-T should transmit only data frames without requiring receptionof ACK frames. At this point, the examples of FIG. 15 and FIG. 16 relateto a method of generating scheduling information for realizing limitedspatial reuse.

Such limited spatial reuse is useful in the following cases. That is, ifa terminal requests data transmission in a period that is not allocated,on the basis of channel measurement information transmitted from thecorresponding request terminal, the control station determines whether areception terminal is able to receive data with no errors. If it isdetermined that the reception terminal is able to receive data with noerrors, the control station additionally allows the request terminal toperform data transmission in a time period allocated in advance. Such ascheduling method may be repeatedly performed until any more additionaldata transmission is not allowed in the time period allocated inadvance. IMPROVEMENT IN EFFICENCY OF SPATIAL REUSE

It is possible to improve the efficiency of spatial reuse by restrictingframe transmission from a destination to a source in an existingresource allocation period and allocating a new resource to overlap theexisting resource allocation period.

FIG. 17 is a drawing illustrating an example of a scheduling method forimproving the efficiency of spatial reuse.

In FIG. 17, the destination may transmit immediate ACK frames, immediateBlockACK frames, or other frames to the source. Here, when the controlstation ties to allocate a new resource for a new terminal pair tooverlap a resource allocated to an existing terminal pair, if framestransmitted by a destination of the existing terminal pair interferewith frame transmission of the new terminal pair, the control stationmay restrict the frame transmission of the destination of the existingterminal pair and allocate the service period for the new terminal pair.In contrast, if frames transmitted by a destination of the new terminalpair interfere with the frame transmission of the existing terminalpair, the control station may restrict the frame transmission of thedestination of the new terminal pair.

FIG. 18 is a drawing illustrating the scheduling method of FIG. 17 inphases.

If determining that the frame transmission of the destination interfereswith the frame transmission of the new terminal pair on the basis of thechannel measurement information, the control station restricts the frametransmission of the destination and allocates the service period for thenew terminal pair. For example, when the existing terminal pair istransmitting frames on the basis of immediate ACK frames or immediateBlockACK frames, transmission of the immediate ACK frames or theimmediate BlockACK frames is prohibited. Instead, in order for ACK, anew resource may be additionally allocated, and in order to use theadditional resource, the immediate ACK policy may be switched to a blockACK policy.

Meanwhile, when the newly added resource is released such that onlyresources for the existing terminal pair is allocated, in order to usethe newly added resource, a block ACK operation may not end. In thiscase, the immediate ACK policy and the block ACK policy may betemporarily used together.

FIG. 19 is a drawing illustrating an example of a field structure ofscheduling information used in the scheduling method of FIG. 17 and FIG.18.

In FIG. 19, a TID (traffic ID) field represents an indenficiation numberfor identifying traffic, and as SPType (service period type) fieldrepresents the type of an allocated service period. A source AID fieldand a destination AID field represent an identification number of asource terminal and an identification number of a destination terminal,respectively, and an SP duration field represents the time length of anallocated resource.

A reverse direction field represents whether a destination can transmitsframes including immediate ACK frames to a resource within an allocatedresource. If it is perceived through the reverse direction field thatthe destination cannot transmit frames to the source within thecorresponding allocated resource, the source and the destination mayswitch the current ACK policy to a predetermined ACK policy. Here, thepredetermined ACK policy may be any kind of ACK policy including a NoACK policy. The destination may transmit information for switching theACK policy to the resource by using other resources allowing frametransmission.

FIG. 20 is a drawing illustrating the structure of information used todetermine the characteristics of traffic for frame transmission.

In FIG. 20, a traffic type field represents the type of traffic and aTSID (traffic stream ID) field represents the dentifier of a trafficstream.

A pseudo-static field represents that resource allocation information isnot transmitted through frames, which may include beacons or resourceallocation information corresponding thereto, every time, and eventhrough the resource allocation information is not transmitted, theresource allocation information does not change.

A truncate field represents that if there is an extra allocatedresource, the allocated resource may be returned, and an extendablefield represents that if allocated resources are insufficient, resourceallocation may be extended. A beamforming training field represents thattraning for beamforming is possible. An UP (user priority) fieldrepresents the priority of traffic that is information to allocate apriority to a user in a competitive channel access scheme.

A dynamic ACK policy field represents that when data transmission of thedestination is prohibited for spatial reuse, switching of the ACK policyis possible.

Hardware Configuration of Control Station

FIG. 21 is a drawing illustrating a configuration of a control station100 according to an exemplary embodiment of the present invention.

In FIG. 21, the control station 100 includes a channel encoder 110, amapper 120, a modulator 130, a reception circuitry 140, a memory 150,and a controller 160.

The channel encoder 110 encodes streams of input information bits by apredetermined coding scheme so as to generate coded data.

The mapper 120 maps the coded data output from the channel encoder 110to symbols represented as positions according to constellations ofphases and amplitudes. A modulation scheme is not limited and may be anm-PSK (m-quadrature phase shift keying) or m-QAM (m-quadrature amplitudemodulation).

The modulator 130 modulates the mapped transmission symbols according toa multiple access modulation scheme. The multiple access modulationscheme is not limited and may be a single-carrier modulation scheme suchas CDMA, or a multi-carrier modulation scheme such as OFDM. Thereception circuitry 140 receives a reception signal through an antenna,digitizes the signal, and transmits the digital signal to the controller160.

The memory 150 stores various kinds of system information necessary forthe operation of the control station 100, scheduling information, andchannel measurement information received from terminals.

The controller 160 controls the general operation of the control station100 and particularly includes a scheduling information generating unit161.

The scheduling information generating unit 161 generates firstscheduling information to define transmission/reception terminals andtransmission time periods, or generates second scheduling information todefine transmission time periods and a plurality oftransmission/reception terminals that do not interfere with each otherby using channel measurement information received by the receptioncircuitry 140. Next, the generated first scheduling information andsecond scheduling information are transmited to the terminals in thenework. A procedure of generating the second scheduling information byusing channel measurement information is the same as described above.

Hardware Configuration of Terminal

FIG. 22 is a drawing illustrating a configuration of a terminal 200according to an exemplary embodiment of the present invention.

In FIG. 22, the terminal 200 includes a channel decoder 210, a demapper220, a demodulator 230, a memory 240, a transmission circuitry 250, anda controller 260.

The demodulator 230, the demapper 220, and the channel decoder 210 ofthe terminal 200 perform inverse functions to the modulator 130, themapper 120, and the channel encoder 110 of the control station 100. Inother words, a signal received through an antenna is demodulated by thedemodulator 230, and is demapped to the coded data by the demapper 220.Next, the coded data is decoded by the channel decoder 210. Thedemodulator 230, the demapper 220, and the channel decoder 210 may begenerally called a reception circuitry (not shown).

The memory 240 stores various kinds of system information necessary forthe operation of the terminal 200, channel measurement informationgenerated by the terminal 200, and scheduling information received fromthe control station 100.

The transmission circuitry 250 receives various kinds of data fromcontroller 260, performs D/A conversion on the data, and transmits thedata to the control station 100 through the antenna.

The controller 260 controls the general operation of the terminal 200and particularly includes a channel measuring unit 261 and aninformation transmitting unit 262.

When the terminal 200 is not defined as a transmission terminal or areception terminal in the scheduling information received form thecontrol station, the channel measuring unit 261 performs transmissionchannel measurement on the transmission terminal and the receptionterminal. The detailed operation of the channel measuring unit 261 isthe same as described in detail in regard to the above-mentionedscheduling method.

The information transmitting unit 262 transmits channel measurementinformation according to the measurement results to the control station.When the terminal 200 is defined as a transmission terminal or areception terminal in the scheduling information, the informationtransmitting unit 262 performs data transmission or ACK messagetransmission in a transmission time period defined in the schedulinginformation. The detailed operation of the information transmitting unit262 such as data transmission or ACK message transmission in a timeperiod allocated in the scheduling information is also the same asdescribed in detail in regard to the above-mentioned scheduling method.

The above-mentioned exemplary embodiments of the present invention arenot embodied only by an apparatus and method. Alternatively, theabove-mentioned exemplary embodiments may be embodied by a programperforming functions that correspond to the configuration of theexemplary embodiments of the present invention. While this invention hasbeen described in connection with what is presently considered to bepractical exemplary embodiments, it is to be understood that theinvention is not limited to the disclosed embodiments, but, on thecontrary, is intended to cover various modifications and equivalentarrangements included within the spirit and scope of the appendedclaims.

What is claimed is:
 1. A method for spatial reuse, comprising: receivingfirst scheduling information requesting at least one terminal in anetwork to perform channel measurement from a control station; measuringa channel based on the first scheduling information, and transmittingchannel measurement information for spatial reuse to the controlstation; and receiving second scheduling information allocating a newresource to overlap an existing resource allocation area to at least oneterminal pair that do not interfere with each other by using the channelmeasurement information.
 2. The method for spatial reuse of claim 1,wherein the channel measurement information includes information on asignal level of the transmission channel.
 3. The method for spatialreuse of claim 1, wherein the second scheduling information includes atleast one of start of the transmission time period, duration of thetransmission time period, the identifier of the transmission terminal,the identifier of the reception terminal, a reason code of transmissiontime period allocation, and the identifier of the transmission timeperiod when channel measurement is performed.
 4. The method for spatialreuse of claim 1, wherein the overlapping resource is time period. 5.The method for spatial reuse of claim 1, wherein existing resourceallocation area is time period.
 6. The method for spatial reuse of claim1, wherein the channel measurement information includes the channelstatus of transmitting/receiving terminals defined in the firstscheduling information.
 7. The method for spatial reuse of claim 1,wherein the control station receives the channel measurement informationfrom a terminal trying to obtain a chance for data transmission by thesecond scheduling information.
 8. The method for spatial reuse of claim1, wherein the control station transmits the first schedulinginformation to the terminals in the network, the first schedulinginformation defining a first terminal to transmit test data in thetransmission time period and a second terminal to measure a transmissionchannel to transmit the test data, and receives the channel measurementinformation from the second terminal.
 9. A terminal for spatial reuse,comprising: a receiving unit configured to receive first schedulinginformation requesting at least one terminal in a network to performchannel measurement from a control station; and a measuring unitconfigured to measure a channel based on the first schedulinginformation, and transmitting channel measurement information forspatial reuse to the control station, wherein the receiver furtherconfigured to receive second scheduling information allocating a newresource to overlap an existing resource allocation area to at least oneterminal pair that do not interfere with each other by using the channelmeasurement information.
 10. The terminal for spatial reuse of claim 9,further comprising an ACK switching unit configured to switch a currentACK message transmission policy to another predetermined ACK messagetransmission policy when the scheduling information includes informationrepresenting that ACK message transmission of the terminal device isrestricted.
 11. The terminal for spatial reuse of claim 9, wherein thechannel measurement information includes information on a signal levelof the transmission channel.
 12. The terminal for spatial reuse of claim9, wherein the second scheduling information includes at least one ofstart of the transmission time period, duration of the transmission timeperiod, the identifier of the transmission terminal, the identifier ofthe reception terminal, a reason code of transmission time periodallocation, and the identifier of the transmission time period whenchannel measurement is performed.
 13. The terminal for spatial reuse ofclaim 9, wherein the overlapping resource is time period.
 14. Theterminal for spatial reuse of claim 9, wherein existing resourceallocation area is time period.